This application claims the priority of Korean Patent Application No. 2002-80032, filed on Dec. 14, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a method of controlling a flash apparatus, and more particularly, to a method of controlling a flash apparatus in which a preliminary flashing is performed, an average brightness of the surroundings is detected in synchronization with a periodic signal subsequent to the preliminary flashing, and a main flashing time is set according to the detected average brightness.
2. Description of the Related Art
FIG. 1 is a block diagram showing the structure of a typical flash control apparatus of a camera. Referring to FIG. 1, a typical flash control apparatus of a digital camera, for example, a digital camera having a model name “Digimax 350SE” manufactured by Samsung Techwin Co., Ltd., includes an image detecting portion IS, an image signal processing portion SP, a timing signal generator TG, and a microcontroller MC.
The image sensing portion IS including a CCD (charge coupled device) or CMOS (complementary metal oxide semiconductor) converts light energy from an object OB to electric energy to generate an image signal in proportion to intensity of flashing of the camera. The image signal processing portion SP processes the image signal from the image sensing portion IS to generate an image signal Yp that is input to the microcontroller MC, and controls the operation of the timing signal generator TG. The timing signal generator TG generates a vertical sync signal VS according to timing control of the image signal processing portion SP and inputs the generated sync signal VS to the image sensing portion IS and the microcontroller MC. The microcontroller MC reads the image signal Yp output from the image signal processing portion SP according to the vertical sync signal VS output from the timing signal generator TG and generates a signal SCFL to control the operation of a flash apparatus FL. The flash apparatus FL includes a light emission driving portion LDR and a light emitting device LE. The light emission driving portion LDR of the flash apparatus FL drives the light emitting device LE according to the control signal SCFL output from the microcontroller MC.
FIG. 2 is a waveform diagram showing a conventional method of controlling the flash control apparatus of FIG. 1, Referring to FIGS. 1 and 2, when a control signal SCFL1 is input to the flash apparatus FL from the microcontroller MC, a preliminary flashing is performed for a short time during a period in which a falling pulse is not generated in the vertical sync signal VS. The preliminary flashing is terminated at a point t1. Next, the microcontroller MC detects an average brightness of the surroundings based on the image signal Yp output from the image signal processing portion SP at a point t2 at which a falling edge of the falling pulse is generated in the vertical sync signal VS. A main flashing time is set and applied in inverse proportional to the detected average brightness. When the preliminary flashing is performed for a relatively short time, with respect to the object OB disposed close to the camera, brightness histogram with respect to pixels of the image sensing portion IS appears to be normal, as shown in FIG. 3A, so that the average brightness of the surroundings is detected accurately. However, with respect to the object OB disposed far from the camera, brightness histogram with respect to the pixels of the image sensing portion IS appears abnormal, as shown in FIG. 3B, so that the average brightness of the surroundings is detected inaccurately.
When a control signal SCFL2 is input to the flash apparatus FL from the microcontroller MC, a preliminary flashing is performed for a long time during a period in which a falling pulse is not generated in the vertical sync signal VS. The preliminary flashing is terminated at a point t1. Next, the microcontroller MC detects an average brightness of the surroundings based on the image signal Yp output from the image signal processing portion SP at the point t2 when a falling edge of the falling pulse is generated in the vertical sync signal VS. A main flashing time is set and applied in inverse proportional to the detected average brightness. When the preliminary flashing is performed for a relatively long time, with respect to the object OB disposed far from the camera, brightness histogram with respect to pixels of the image sensing portion IS appears to be normal, as shown in FIG. 4A, so that the average brightness of the surroundings is detected accurately. However, with respect to the object OB disposed close to the camera, brightness histogram with respect to the pixels of the image sensing portion IS appears abnormal, as shown in FIG. 4B, so that the average brightness of the surroundings is detected inaccurately.
Thus, according to the above typical control method, the preliminary flashing is needed at least two times, as shown in the waveform of a control signal SCFL3 When the flash apparatus FL is operated according to the control signal SCFL3, the short preliminary flashing is terminated at the point t1 and a first average brightness is detected at the point t2 when a falling edge of the first pulse is generated in the vertical sync signal VS. The long preliminary flashing is terminated at a point t3 and a second average brightness is detected at a point t4 at which a falling edge of the second pulse is generated in the vertical sync signal VS. According to the typical control method, since at least two times preliminary flashing are needed, power consumption of the flash apparatus FL increases while the life span thereof decreases.